Study On The Mechanism Of Interfacial Inducing And Controlling Of PLA/Bio-polyester Blends Containing Ionic Liquid Oligomers With Specific Structures

Owing to the intrinsic thermodynamically immiscibility of poly(lactic acid)(PLA)with other biodegradable polyester elastomers,additional compatibilizer,such as block copolymer and phase interface crosslinker,often used to regulate the interface of PLA-based blends.The research mainly focused on the effects of the structure and amounts of compatibilizer on the properties of the corresponding blends,however,the mechanism of interfacial regulation for the PLA blends are rare reported.In this dissertation,1,2,3-triazole-clicked PCL-b-PEG block copolymer(TAPEC)and its ionized ionomer TAPEC(IL)were firstly synthesized,and then blended with PLA to study the effects of TAPEC and TAPEC(IL)on the formation of PLA aggregation state.Then TAPEC and TAPEC(IL)were introduced into the PLA/PCL blend system to explore the effect on the interface of PLA/PCL components and the mechanical properties of the blends.In addition,based on the luminescent properties of rare-earth element,electrostatic complex(Eu-ILOI)based on triblock ionomer'(ILOI)and polyoxometalate(EuW10)were designed and synthesized to explore the mechanism of interfacial inducing and controlling of PLA/PCL blends containing Eu-ILOI.Based on these,the enhanced compatibilization mechanism of PLA/EMA-GMA blends and PLA/EMA-GMA/ILs/MWCNTs nanocomposites were studied as well.1)The copolymers TAPEC and TAPEC(IL)containing PCL and PEG segments were synthesized,and the effects of TAPEC and TAPEC(IL)on the evolution of the matrix structures of PLA blends were studied by DSC,XRD,POM and SEM.The results showed that the effects of TAPEC on the PLA is similar to traditional plasticizers,however,the ionic moieties in the TAPEC(IL)promote its compatibility with PLA,and induce TAPEC(IL)to form the lowest energy styles such as "ion pairs" and "ion clusters" in PLA matrix.The "ion pairs" and "ion clusters" can promote the nucleation of PLA and improve the mobility of PLA chain segment at the same time.More importantly,isothermal crystallization kinetics analysis results manifested that the synergistic effect of heterogeneous nucleation agent of ionic cluster of TAPEC(IL)and chain mobility promoter of PEG chain segment,which could enhance the crystallization ability of the PLA at all crystallization temperature.The XRD results show that the crystalline form of PLA shifts to stable ? crystal when the content of TAPEC(IL)increased to 5wt%.2)Taking advantage of the characteristics of ionic liquid and block copolymer,TAPEC and TAPEC(IL)are expected to be used as a novel compatibilizer in mixed bio-polyester for regulating the interface and crystallization behaviors.The study found that TAPEC promoted the aggregation of PCL,and with the increase of its content,the degree of PCL aggregation increased.The ionic moieties in TAPEC(IL)endowed it with a strong interfacial emulsification capacity,and increased the dispersion of PCL in the PLA matrix.Hence,the TAPEC(IL)was evaluated as a compatibilizer and interface emulsifier in the PLA/PCL blends.Non-isothermal crystallization experimental results showed that the TAPEC with the higher amount of ?-caprolactone units induce a plasticization and nucleate effect that increases the crystallization ability of the PLA phase,Meanwhile in the PCL phase the agminated ionic cluster that act as a nucleating agent significantly increased the crystalline of PCL and ultimately improved the mechanical properties of the PLA/PCL blends.3)Taking advantage of the characteristic luminescent properties of rare-earth element,a novel europium containing complex(Eu-ILOI)were designing and synthesized,acting as luminescent probes to trace the interface formation process of PLA/PCL blends.The Raman spectroscopy and TEM results indicated that luminescence is mainly concentrated on the PLA/PCL interface and in the PCL phase.When small amount of Eu-ILOI was added,it can induce the nucleation of PLA,acting as an interfacial emulsifier to significantly increase the crystalline of PCL.However,as the content of Eu-ILOI exceeds to 0.7 wt%,the Eu-ILOI can self-assemble into a "micellar layer"covering the surface of PCL micelles through the non-covalent bond between the Eu-ILOI segments and enhances the interaction between PLA and PCL macromolecular chains.At the same time high amount of the non-covalent bonding forces can limit the movement of the PCL and PLA segments and inhibit their crystallization ability.Dielectric tests also indicate that the introduction of Eu-ILOI can achieve the dielectric polarization tracing of PLA/PCL blends.4)In PLA/EMA-GMA incompatible blend system,the dispersion of EMA-GMA and the interaction between PLA and EMA-GMA molecular chain have an important influence on the properties of materials.Accordingly,1-carboxymethyl-3-methylimidazolium bromide(ILs)were used as an interfacial modulating catalyst,and the effects of ILs on the interfacial properties of PLA/EMA-GMA blends were investigated using a flat panel rheometer,DSC,SEM,and a dynamic mechanical analyzer(DMA).The results show that ILs can catalyze the interface compatibilization of PLA/EMA-GMA,and increase the reaction extent of PLA and EMA-GMA,which can induce the phase structure of the blends transformed from"island structure" to "double-continuous structure".When the content of ILs exceeded 2 wt%,a three-dimensional network structure is formed inside material which leads to increasing viscosity and elasticity.Consenquently,the mechanical properties of the PLA materials are improved significantly.For example,the materials exhibit improvements by a factor of 71 in tensile toughness and a factor of 22 in notched Izod impact strength at the optimum ILs content.5)The mechanism of phase structure and interfacial enhanced compatibilization of PLA/EMA-GMA/multi walled carbon nanotube(MWCNTs)nanocomposite system regulated by ILs were studied by SEM,DSC,rheometer and LRC.It "was found that the compatibility between MWCNTs and matrix is poor,and the ILs can improve the dispersion performance of MWCNTs in matrix and increase the interaction force between MWCNTs and matrix.The crystallization performance of PLA was improved as well.The rheological tests showed that the G' of the samples increased and G"decreased after the ILs are introduced into the nanocomposite system,which indicating that the ILs can catalyze the formation of the continuous crosslinked network structure inside the nanocomposite.When the content of ILs and MWCNTs reached to 2 wt%and 4 wt%,respectively,the interfacial polarization in the dielectric constant is significantly enhanced,and the enhancement of interfacial adhesion force significantly suppressed dielectric loss.Compared with PLA/EMA-GMA/4C material,the PLA/EMA-GMA/4C/2I composites that was fabricated by melt blending method can achieve excellent mechanical and dielectric properties(tensile strength 27MPa,elongation at break 63%,and at 100Hz,dielectric constant 32,dielectric loss 0.08).